U.S. patent application number 13/675769 was filed with the patent office on 2013-05-30 for method of producing radioactive molybdenum.
This patent application is currently assigned to JAPAN ATOMIC ENERGY AGENCY. The applicant listed for this patent is JAPAN ATOMIC ENERGY AGENCY. Invention is credited to Hiroaki AKIYAMA, Takuya ISHIDA, Akihiro KIMURA, Shigeru KITAGISHI, Masaaki NAGAKURA, Kaori NISHIKATA, Kunihiko SUZUKI, Kunihiko TSUCHIYA.
Application Number | 20130136221 13/675769 |
Document ID | / |
Family ID | 48466864 |
Filed Date | 2013-05-30 |
United States Patent
Application |
20130136221 |
Kind Code |
A1 |
NISHIKATA; Kaori ; et
al. |
May 30, 2013 |
METHOD OF PRODUCING RADIOACTIVE MOLYBDENUM
Abstract
To provide a method of producing radioactive molybdenum solution
suitable for extracting .sup.99mTc to be used as radioactive
diagnostic drug by way of establishing a production process for
high-density MoO.sub.3 pellets with a lower amount of insoluble
content when dissolving the pellets. The method has the steps of:
preparing MoO.sub.3 powder, fabricating a MoO.sub.3 pellet by
filling said MoO.sub.3 powder in a heated die and sintering in an
air, oxidizing said MoO.sub.3 pellet, producing neutron-irradiated
MoO.sub.3 pellets by irradiating a neutron on said oxidized
MoO.sub.3 pellet, and obtaining radioactive molybdenum solution by
dissolving said neutron-irradiated MoO.sub.3 pellet.
Inventors: |
NISHIKATA; Kaori;
(Higashi-ibaraki, JP) ; KIMURA; Akihiro;
(Higashi-ibaraki, JP) ; ISHIDA; Takuya;
(Higashi-ibaraki, JP) ; KITAGISHI; Shigeru;
(Higashi-ibaraki, JP) ; TSUCHIYA; Kunihiko;
(Higashi-ibaraki, JP) ; AKIYAMA; Hiroaki; (Hiki,
JP) ; NAGAKURA; Masaaki; (Hiki, JP) ; SUZUKI;
Kunihiko; (Hiki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JAPAN ATOMIC ENERGY AGENCY; |
Ibaraki |
|
JP |
|
|
Assignee: |
JAPAN ATOMIC ENERGY AGENCY
Ibaraki
JP
|
Family ID: |
48466864 |
Appl. No.: |
13/675769 |
Filed: |
November 13, 2012 |
Current U.S.
Class: |
376/186 |
Current CPC
Class: |
G21G 1/06 20130101; G21G
2001/0036 20130101; G21G 1/001 20130101 |
Class at
Publication: |
376/186 |
International
Class: |
G21G 1/00 20060101
G21G001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 14, 2011 |
JP |
2011248993 |
May 29, 2012 |
JP |
2012121785 |
Claims
1. A method of producing radioactive molybdenum solution comprising
a step of preparing MoO.sub.3 powder, a step of fabricating a
MoO.sub.3 pellet by filling said MoO.sub.3 powder in a heated die
and sintering in an air, a step of oxidizing said MoO.sub.3 pellet,
a step of producing neutron-irradiated MoO.sub.3 pellets by
irradiating a neutron on said oxidized MoO.sub.3 pellet, and a step
of obtaining radioactive molybdenum solution by dissolving said
neutron-irradiated MoO.sub.3 pellet.
2. The method of producing radioactive molybdenum solution
according to claim 1, wherein said step of oxidizing said MoO.sub.3
pellet is performed by means that said MoO.sub.3 pellet is exposed
in ozone gas at a reaction temperature range grater than equal to a
room temperature and less than 120.degree. C. or baked
preliminarily in an air at a temperature equal to or more than
350.degree. C. and less than 500.degree. C.
3. The method of producing radioactive molybdenum solution
according to claim 1, wherein said step of obtaining radioactive
molybdenum solution by dissolving said neutron-irradiated MoO.sub.3
pellet is performed by using a dissolving apparatus with ultrasonic
device for said neutron-irradiated MoO.sub.3 pellet in 6M NaOH
solution.
4. A method of producing radioactive molybdenum solution comprising
a step of preparing MoO.sub.3 powder, a step of fabricating a
MoO.sub.3 pellet by sintering said MoO.sub.3 powder in a heated die
in an air at a temperature equal to or more than 500.degree. C. and
less than 540.degree. C. by a plasma sintering method, a step of
oxidizing said MoO.sub.3 pellet, a step of producing a
neutron-irradiated MoO.sub.3 pellet by irradiating a neutron on
said oxidized MoO.sub.3 pellet, and a step of obtaining radioactive
molybdenum solution by dissolving said neutron-irradiated MoO.sub.3
pellet.
5. The method of producing radioactive molybdenum solution
according to claim 4, wherein said step of oxidizing said MoO.sub.3
pellet is performed by means that said MoO.sub.3 pellet is exposed
in ozone gas at a reaction temperature range grater than equal to a
room temperature and less than 120.degree. C. or baked
preliminarily in an air at a temperature equal to or more than
350.degree. C. and equal to or less than 500.degree. C.
6. The method of producing radioactive molybdenum solution
according to claim 4, wherein said step of obtaining radioactive
molybdenum solution by dissolving said neutron-irradiated MoO.sub.3
pellet is performed by using a dissolving apparatus with ultrasonic
device for said neutron-irradiated MoO.sub.3 pellet in 6M NaOH
solution.
7. The method of producing radioactive molybdenum solution
according to claim 5, wherein said step of obtaining radioactive
molybdenum solution by dissolving said neutron-irradiated MoO.sub.3
pellet is performed by using a dissolving apparatus with ultrasonic
device for said neutron-irradiated MoO.sub.3 pellet in 6M NaOH
solution.
Description
BACKGROUND OF THE INVENTION
[0001] Present invention relates to a method of producing
radioactive molybdenum (.sup.99Mo) as the parent nuclide of
technetium-99m (.sup.99mTc), a radioactive diagnostic drug
indispensable for the image diagnosis of diseases such as cancer,
myocardial infarction, cerebral apoloplexy and others, by neutron
irradiation with .sup.98Mo as the raw material.
[0002] .sup.99mTc may be generated due to .beta..sup.- decay of
.sup.99Mo as its parent nuclide. (n, .gamma.) method of producing
.sup.99Mo by neutron irradiation with .sup.98Mo being as the raw
material is known as one of the methods for producing .sup.99Mo.
(n, .gamma.) method is such a method that a solid substance
including natural molybdenum (for example, MoO.sub.3 pellet) may be
placed inside the irradiation container (hereinafter referred to as
"rabbit"), and in a nuclear reactor, and then .sup.99Mo may be
produced due to neutron capture reaction (.sup.98Mo (n, .gamma.)
.sup.99Mo reaction).
[0003] In the production of radioactive molybdenum (.sup.99Mo) by a
(n, .gamma.) method, in which the processes after neutron
irradiation include at most an extraction of MoO.sub.3 pellet from
the rabbit and a dissolution of the pellets, there is such an
advantage that the amount of radioactive waste is smaller in
contrast to (n, f) method, which is one of the other production
methods for radioactive molybdenum. The production cost of
.sup.99Mo is as low as 0.83 US$ for 37 GBq. However, as the
fraction of .sup.99Mo generated by the (n, .gamma.) method may be
reduced due to the existence of molybdenum elements with the
different mass numbers, its specific radioactivity is
disadvantageously from 37 to 74 GBq/g-Mo being lower than that in
(n, f) method. This is the reason why it is required to increase
the production amount of .sup.99Mo.
[0004] In order to increase the production amount of .sup.99Mo, it
is required to make the best use of high-density MoO.sub.3 pellets
as the irradiation target for the various reasons. As for the
production method of MoO.sub.3 pellets, what have been used are
several methods including uniaxial pressing method, hot pressing
method, hot isostatic pressing method, and plasma sintering method
and others. For example, Patent Document 1, which discloses an
invention aimed for achieving the similar object to that of the
present invention, discloses a method of producing high-density
MoO.sub.3 pellets by Spark Plasma Sintering (SPS) method, one of
plasma sintering methods. In the method according to Patent
Document 1, high-density MoO.sub.3 pellets may be produced by SPS
method under the condition for the sintering temperature from 540
to 640.degree. C. in a vacuum.
[0005] [Patent Document 1] JP 2010-175409 A
BRIEF SUMMARY OF THE INVENTION
[0006] In general, there is such a disadvantage as low sintering
density in MoO.sub.3 pellets produced by uniaxial pressing method,
hot-press method and hot isostatic pressing method, being used
generally as the production method of ceramics. In those methods,
it is also required to add binders such as camphor, polyvinyl
alcohol (PVA) and the like when forming MoO.sub.3 pellets, which
may leads to some potential for impurities being mixed in MoO.sub.3
pellets. Though MoO.sub.3 pellets produced by SPS method may have
the sintering density as high as about 95% as disclosed in Patent
Document 1, this method may be not always satisfactory for
extracting .sup.99mTc to be used as the diagnostic drug because of
such problems that a longer duration time may be required for
dissolving high-density MoO.sub.3 pellets produced according to
this method with sodium hydroxide (NaOH) solution, and that there
may remain a large amount of insoluble content.
[0007] An object of the present invention is to provide a method of
producing radioactive molybdenum solution suitable for extracting
.sup.99mTc to be used as the radioactive diagnostic drug by way of
establishing a production process for high-density MoO.sub.3
pellets with a lower amount of insoluble content when dissolving
the pellets.
[0008] In one aspect of the present invention, the production
method of radioactive molybdenum solution comprises five steps
including; a step of preparing MoO.sub.3 powder, a step of
fabricating MoO.sub.3 pellets by sintering said MoO.sub.3 powder in
a heated die, a step of oxidizing said MoO.sub.3 pellets, a step of
producing neutron-irradiated MoO.sub.3 pellets including .sup.99Mo
by neutron irradiation on said oxidized MoO.sub.3 pellets, and a
step of obtaining radioactive molybdenum solution by dissolving
said neutron-irradiated MoO.sub.3 pellets.
[0009] What is provided is a producing method of radioactive
molybdenum solution in which the step of oxidizing MoO.sub.3
pellets obtained in said fabricating step enables to reduce the
amount of insoluble content as much as possible by means that
MoO.sub.3 pellets may be exposed in ozone gas at the reaction
temperature range equal to or higher than the room temperature or
equal to or less than 120.degree. C., or baked preliminarily in the
air at the temperature equal to or higher than 350.degree. C. and
equal to or less than 500.degree. C.
[0010] In another aspect of the present invention, a producing
method of radioactive molybdenum solution includes a step of
preparing MoO.sub.3 powder, a step of fabricating MoO.sub.3 pellets
by sintering said MoO.sub.3 powder in a heated die in the air at
the temperature equal to or more than 500.degree. C. and less than
540.degree. C. by plasma sintering method, a step of oxidizing said
MoO.sub.3 pellets, a step of producing neutron-irradiated MoO.sub.3
pellets by irradiating neutrons on said oxidized MoO.sub.3 pellets,
and a step of obtaining radioactive molybdenum solution by
dissolving said neutron-irradiated MoO.sub.3 pellets.
[0011] Either of an SPS method or a Plasma Activated Sintering
(PAS) method may be applied as plasma sintering method used in the
present invention, in which MoO.sub.3 pellets may be sintered in
the air.
EFFECT OF THE INVENTION
[0012] According to the present invention, it will be appreciated
that the amount of insoluble content may be reduced substantially,
and that a high-quality radioactive diagnostic drug may be obtained
finally by means that a step of oxidizing the fabricated MoO.sub.3
pellets after fabricating MoO.sub.3 pellets is placed as the
preceding step before the step of obtaining radioactive molybdenum
solution by dissolving said neutron-irradiated MoO.sub.3
pellets.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a flow chart illustrating the method of producing
radioactive molybdenum solution.
[0014] FIG. 2 is a schematic diagram of an apparatus for sintering
MoO.sub.3 pellets by a plasma sintering method.
[0015] FIG. 3 is a graph showing the correlation between the
sintering density and the sintering temperature in MoO.sub.3
pellets when applying the plasma sintering method.
[0016] FIG. 4 is a schematic diagram of an apparatus for oxidizing
MoO.sub.3 pellets.
[0017] FIG. 5 is a graph showing the temperature dependency of
Ozone gas concentration.
[0018] FIG. 6 is a schematic diagram of an apparatus for dissolving
neutron-irradiated MoO.sub.3 pellets.
[0019] FIG. 7 is a table showing the test result of oxidization
process by using ozone gas exposure and dissolving process of
MoO.sub.3 pellets.
[0020] FIG. 8 is a table showing the characteristic test result of
oxidization process of MoO.sub.3 pellets in the high-temperature
air.
[0021] FIG. 9 is a photograph of MoO.sub.3 pellets finished by
oxidization process in the air at 350.degree. C. for two hours and
the solution in which MoO.sub.3 pellets are dissolved by 6M
NaOH.
DETAILED DESCRIPTION OT THE INVENTION
[0022] Referring to FIG. 1, the outline of a method of producing
radioactive molybdenum (.sup.99Mo) solution is described. In Step
1, MoO.sub.3 powder is prepared (S101). As for such MoO.sub.3
powder, for example, high-purity MoO.sub.3 powder (99.99% (4N)),
MoO.sub.3 powder containing enriched .sup.98Mo intended for
increasing the amount of produced .sup.99Mo and the like may be
used. In Step 2, MoO.sub.3 powder is sintered in the air by a
plasma sintering method (SPS method or PAS method) in order to
obtain high-density MoO.sub.3 pellets (S102). In Step 3, MoO.sub.3
pellets are oxidized in order to reduce the amount of insoluble
content in the dissolving process in the final step (S103). In Step
4, oxidized MoO.sub.3 pellets are irradiated with neutrons, for
example, in the nuclear reactor in order to produce
neutron-irradiated MoO.sub.3 pellets (S104). In the last Step,
neutron-irradiated MoO.sub.3 pellets are dissolved in a sodium
hydroxide (NaOH) solution in order to obtain radioactive molybdenum
solution (S105). The detail of each step will be described
below.
[0023] Steps 1 though 5 may be performed, for example, at the
neutron irradiation facility and its associated facility capable of
handling radioactive materials. The obtained radioactive molybdenum
solution may be then transferred directly through pipes to the
process for extracting .sup.99mTc, or .sup.99Mo may be adsorbed by
Mo adsorbent, and then a glass-based column may be filled with Mo
adsorbent holding .sup.99Mo and inserted in the dedicated container
having a shielding function, and then the dedicated container may
be delivered to the hospital in order to be used as the radioactive
diagnosis drug. In case of large-scale general hospital, it is
allowed to provide the hospital with the facility capable of
implementing the method of producing radioactive molybdenum
according to the present invention. .sup.99mTc generated by
beta-decay may be extracted and used for cancer diagnosis at the
hospital, the detail of which is not described here.
[Fabrication Steps of High-Density MoO.sub.3 Pellets]
[0024] By referring to FIG. 2, what will be described next is the
step of fabricating high-density MoO.sub.3 pellets by means of
plasma sintering method as in Step 2 (S102) shown in FIG. 1. The
sintering apparatus, shown in FIG. 2, used for fabricating
high-density MoO.sub.3 pellets is composed of a container for
storing raw material powder to be filled into the sintering mold, a
uniaxial pressing mechanism, a raw material heating system and an
electrode system capable of applying a pulsed current, and other
mechanisms and systems. The temperature inside the mold may be
measured by the thermocouple inserted through holes provided at the
mold. Such a sintering apparatus used for a plasma sintering method
has been known to those skilled in the art, the structure of which
is not described in detail here.
[0025] Fabricating of MoO.sub.3 pellets by m ns of a plasma
sintering method is advantageously characterized by that the
sintering process in the air may be allowed and the reduction
action in the sintering process may be made suppressed as much as
possible.
[0026] Though the sintering process only in the vacuum condition
have been employed conventionally in producing MoO.sub.3 pellets by
SPS method, the present invention establishes the sintering process
in the air by providing a gas flow part capable of importing and
carrying the air. An example of the sintering condition of
MoO.sub.3 pellet having the dimension of 20.times.10 mm will be
described below. A certain amount of MoO.sub.3 powder may be filled
and then pressurized. After pressurization, the temperature is made
increase up to a certain sintering temperature while removing the
moisture and oxygen exiting on the surface of powder particle by
applying a certain level of current, and then upon the temperature
reaches a certain level of temperature and keeps its value
constant, the temperature may be maintained to be constant for 5
minutes. After completing the above processes, the finished
MoO.sub.3 pellets were removed and forwarded to the characteristic
evaluation process.
[0027] Fabrication of MoO.sub.3 pellets by PAS method is
advantageously characterized by that the sintering process in the
air has been allowed conventionally, and that applying a pulsed
current before the sintering process may bring such an effect that
the sintering properties among powder particles may be increased.
An example of the sintering condition of MoO.sub.3 pellet having
the dimension of .phi. 20.times.10 mm will be described below. A
certain amount of MoO.sub.3 powder may be filled and then
pressurized. After pressurization, a voltage about 2V may be
applied in the form of square wave pulse with its width 100 ms for
about 30 seconds in the room temperature. Owing to this process,
the moisture and oxygen exiting on the surface of powder particle
can be removed. Next, the temperature is made increase to a certain
level of sintering temperature while applying voltage and current,
and then, and then upon the temperature reaches a certain level of
temperature and keeps its value constantly, the temperature may be
maintained for 5 minutes. After completing the above processes, the
finished MoO.sub.3 pellets were removed and forwarded to the
characteristic evaluation process.
[0028] FIG. 3 shows the measurement result of sintering
characteristic of MoO.sub.3 pellets so obtained in the production
processes for MoO.sub.3 pellets by plasma sintering method, in
which the pressure, voltage and current levels are made constant
while the sintering temperature is made change as a parameter. FIG.
3 illustrates the sintering-temperature dependency of sintering
density in MoO.sub.3 pellets. Based on the data shown in FIG. 4, it
is proved that by means of choosing such a process condition that
the sintering temperature is made equal to or higher than
500.degree. C. or less than 540.degree. C. in the air for SPS
method and PAS method, respectively, high-density MoO.sub.3 pellets
with the sintering density being 90% T.D. (Theoretical Density) may
be obtained which can provide the amount of produced .sup.99Mo
about 30% more in contrast to MoO.sub.3 pellets produced by
uniaxial pressurization molding method. This means that the target
sintering density can be attained with the temperature lower than
the temperature described in Patent Document 1.
[Low-Temperature Ozone Oxidization Process for MoO.sub.3
Pellets]
[0029] FIG. 4 shows a schematic diagram of the apparatus for
oxidizing MoO.sub.3 pellets with ozone according to the present
invention. The oxidizing apparatus includes an ozone generator for
accelerating the oxidation of MoO.sub.3 pellets. MoO.sub.3 pellets
are inserted into the vessel loaded inside the thermostatic oven
for controlling the reaction temperature, which has the structure
enable to establish the reaction with ozone by flowing ozone from
the ozone generator. Ozone exhausted from the reaction vessel in
the thermostatic oven may flow through the ozone monitor and the
ozone killer, and finally be exhausted from the apparatus.
MoO.sub.3 pellets were oxidized with ozone by using the oxidizing
apparatus.
[0030] As ozone gas has a strong oxidization capacity, its
oxidization reaction has been mainly used for oxidization of
organic materials. In contrast, though functional ceramics has been
developed recently as inorganic oxide, there is little exemplary
experience in using ozone gas for its oxidization process. In
studying the oxidization process of ceramics in order to estimate
the ozone density dependent of the reaction temperature, the
performance of the apparatus according to the present invention was
tested (refer to FIG. 5). According to the test result, it is
proved that ozone begins to be resolved when the temperature inside
the thermostatic oven becomes equal to or higher than 120.degree.
C., and that there remains little ozone at about 180.degree. C. and
thus, the oxidization effect will disappear.
[0031] Based on the test result shown by the graph in FIG. 5,
high-density MoO.sub.3 pellets fabricated by plasma sintering
method were made oxidized substantially. The conditions for
oxidization process are specified as below.
(1) MoO.sub.3 pellets: high-density MoO.sub.3 pellets (about 95%
T.D.) (2) Reaction Duration Time: 1, 2 and 20 hours (3) Reaction
Temperature: room temperature, 50, 80, 100, 120 and 150.degree.
C.
[0032] High-density MoO.sub.3 pellets fabricated by plasma
sintering method were easily oxidized in the exposure temperature
range from room temperature to 120.degree. C. It is proved that
this oxidization process is almost independent of the exposure
temperature but dependent of the ozone gas density. As for the
exposure time, the longer the reaction time, the deeper the
oxidation process reaches the inside of pellets.
[Oxidization Process for MoO.sub.3 Pellets in the High-temperature
Air]
[0033] As the sublimation of MoO.sub.3 starts at the temperature
about 650.degree. C. or higher, the condition for the oxidization
process in the air for MoO.sub.3 pellets according to the present
invention was specified first. MoO.sub.3 pellets may be oxidized in
the air in such configuration that MoO.sub.3 pellets are placed on
the ceramics-based dish installed inside the electric furnace for
controlling the oxidization temperature, and a thermocouple for
fabricating the temperature is arranged near MoO.sub.3 pellets.
[0034] In general, the oxidization process for ceramics is
performed in the oxygen gas or in the air at a higher temperature.
However, as for the ceramics sublimated in a lower temperature, the
oxidization process for such ceramics in a higher temperature
easily affects its sintering density and crystal structure.
Therefore, the condition for oxidization process with ozone gas in
the lower temperature as described above and also the condition for
the higher temperature which is recognized to be important were
specified for the oxidization performance test of MoO.sub.3
pellets. The temperature condition for oxidization characteristics
test may be specified in terms of the temperature range from
180.degree. C. at which the oxidization effect by using ozone may
disappear to 650.degree. C. at which the sublimation of MoO.sub.3
pellets may start, and then high-density MoO.sub.3 pellets
fabricated by plasma sintering method were made oxidized
substantially in the high-temperature air. The conditions for
oxidization process are specified as below.
(1) MoO.sub.3 pellets: high-density MoO.sub.3 pellets (about 95%
T.D.) (2) Reaction Duration Time: 2 hours
(3) Reaction Temperature: 200, 300, 350, 400, 500, and 600.degree.
C.
[0035] It was found difficult to oxidize high-density MoO.sub.3
pellets fabricated by plasma sintering method under the condition
of the temperature range from 200 to 300.degree. C. and the
duration time of 2 hours, and it was also observed that the surface
color of MoO.sub.3 pellets does not change significantly at all
before and after the oxidization process. In contrast, for
MoO.sub.3 pellets fabricated by a plasma sintering method under the
condition of the temperature range from 400 to 500.degree. C. and
the duration time of 2 hours, it was observed that the surface of
MoO.sub.3 pellets changes color to white after the oxidization
process. In order to study the boundary temperature between 300 and
400.degree. C. for such color change, the oxidization process was
performed under the condition of the temperature at 350.degree. C.
and the duration time of 2 hours, it was also observed that the
surface of MoO.sub.3 pellets changes color to white after the
oxidization process. Based on the measurement of sintering density
of MoO.sub.3 pellets and the observation of crystal grain in
MoO.sub.3 pellets with the Scanning Electron Microscopy (SEM), it
was proved that the sintering density of MoO.sub.3 pellets does not
change before and after the oxidization process and also that the
growth of crystal grain was not found. In contrast, as for the
oxidization process under the condition of the temperature at
600.degree. C., and the duration time of 2 hours, it was observed
that the surface of MoO.sub.3 pellets changes color to white and
the sintering density does not change, respectively, after the
oxidization process, but that the growth of crystal grain was found
after the oxidization process for MoO.sub.3 pellets.
[0036] As the result of studies as described above, it is proved
that ozone gas is a better selection at the lower temperature
range, and that the temperature of the oxidization process for
high-density MoO.sub.3 pellets may be optimized by selecting to be
equal to or higher than the room temperature, or equal to or less
than 120.degree. C. in which the ozone gas density does not change.
In addition it is proved that the sublimation of MoO.sub.3 never
starts in the air at the higher temperature range, and hence that
the oxidization process at the higher temperature range may be
optimally performed in the temperature range equal to or higher
than 350.degree. C., or equal to or less than 500.degree. C. in
which MoO.sub.3 is not sublimated in the air and the growth of
crystal grain in MoO.sub.3 pellets is not found.
[Production of Neutron-Irradiated MoO.sub.3 Pellets]
[0037] High-density MoO.sub.3 pellets finished with the oxidization
process may be loaded in the rabbit and irradiated with neutrons,
for example, in the nuclear reactor. As the result,
neutron-irradiated MoO.sub.3 pellets including (n,
.gamma.).sup.99Mo, or simply .sup.99Mo, may be produced. As the
half-life of .sup.99Mo so obtained is as short as about 66 hours,
it is required to complete the subsequent dissolving step in a
short period of time if at all possible.
[Production of Molybdenum Solution from High-Density MoO.sub.3
Pellets]
[0038] FIG. 6 shows a schematic diagram of the dissolving apparatus
for high-density MoO.sub.3 pellets. The dissolving apparatus is
provided with an ultrasonic device for accelerating the dissolving
process of neutron-irradiated MoO.sub.3 pellets, and a resolver for
neutron-irradiated MoO.sub.3 pellets is loaded in the ultrasonic
device. What is provided is such a system that radioactive
molybdenum solution obtained by dissolving neutron-irradiated
MoO.sub.3 pellets may be easily transported via a pump to
.sup.99mTc extraction step. By using the developed dissolving
apparatus with an ultrasonic device for MoO.sub.3 pellets, a
dissolution test was carried out by using MoO.sub.3 pellets
finished with the low-temperature ozone oxidization process and 6M
NaOH solution. FIG. 7 shows the dissolution test result. In the
dissolution test, the frequency of ultrasonic wave was made 40 kHz,
and thus the temperature at the dissolving process increased
gradually up to about 60.degree. C. due to the reaction heat caused
by the dissolution of MoO.sub.3 pellets in NaOH solution.
[0039] After MoO.sub.3 pellets were exposed to ozone gas, MoO.sub.3
pellets were dissolved in 6M NaOH solution. The color of molybdenum
solution obtained by dissolving MoO.sub.3 pellets not exposed to
ozone gas changes to olive, which demonstrates that insoluble
content exists. In contrast, the color of molybdenum solution
obtained by dissolving MoO.sub.3 pellets to ozone gas at the
temperature at 150.degree. C. changes to pale orange, which
demonstrates that an insoluble content still exists though its
volume is less than the insoluble content in the molybdenum
solution obtained without exposure to ozone gas. As for MoO.sub.3
pellets finished with the oxidization process in the exposure
temperature to ozone gas controlled to be from room temperature to
120.degree. C. which does not affect the ozone gas density, the
color of molybdenum solution obtained with oxidization process for
2 and 20 hours, respectively, is maintained to be clear in
comparison with the molybdenum solution obtained without
oxidization process, which demonstrates that no insoluble content
exists.
[0040] By using a dissolving apparatus with an ultrasonic device
for MoO.sub.3 pellets and using 6M NaOH solution, a dissolution
test was performed for MoO.sub.3 pellets finished with the
oxidization process at a higher temperature in the air under the
similar condition to that for MoO.sub.3 pellets finished with the
oxidization process at a lower temperature. The test results are
shown in FIG. 8 and FIG. 9.
[0041] After finishing MoO.sub.3 pellets with oxidization process
at a higher temperature in the air, MoO.sub.3 pellets were made
dissolved in 6M NaOH solution. The color of molybdenum solution
obtained by dissolving MoO.sub.3 pellets not oxidized, and the
color molybdenum solution obtained by dissolving MoO.sub.3 pellets
finished with the oxidization process at the temperature range from
200 to 300.degree. C. for 2 hours changed to olive, which
demonstrates that an insoluble content exists. The color of
molybdenum solution obtained by dissolving MoO.sub.3 pellets
finished with the oxidization process at the temperature equal to
or higher than 350.degree. C. for 2 hours is maintained to be
clear, which demonstrates that no insoluble content exists. Note
that FIG. 8 only shows that the data for the particle with its
average diameter 3 .mu.m and that the same test result was obtained
independent of the average particle diameter.
* * * * *